1. Field of the Invention
The present invention relates to a multilayered chip-type inductance-capacitance (LC) composite component, and it particularly relates to an LC composite component obtained by monolithically sintering a capacitor portion and an inductor portion.
2. Description of the Related Art
A multilayered chip-type LC composite component obtained by combining an inductor and a capacitor is used in, for example, a passive filter. The LC composite component comprises, as the main body of the component, a multilayered structure obtained by layering green sheets of a magnetic material and a dielectric material in turn, and by then monolithically sintering the resulting structure. More specifically, magnetic ceramic portions which provide the inductor and dielectric portions which provide the capacitor are superposed in turn, and the resulting structure is monolithically sintered thereafter.
Although there are various types of dielectric ceramic materials, not all can be used directly in the monolithic sintering with a magnetic ceramic material. However, to meet for a wide variety of applications, the use of a still increasing variety of dielectric ceramic materials in LC composite components is strongly requested.
To meet for the demand above while employing the technology for monolithically sintering a dielectric ceramic portion and a magnetic ceramic portion, it is necessary to permanently achieve favorable joint between the different type of materials. This can be accomplished by controlling the sintering behavior and the diffusion species as well as by controlling the stress, which generates at the joint interface on cooling from the sintering temperature to room temperature, to a value not higher than the breaking point of both dielectric and magnetic ceramics. Techniques related to these are disclosed in, for instance, the following literature.
In Unexamined Published Japanese Patent Application No. 64-61015 is disclosed a technique of incorporating a borosilicate glass in the ceramic dielectric layer so as to approximate the linear expansion coefficient of the ceramic dielectric layer to that of the ceramic magnetic layer. The addition of a glass component in this case is aimed to relax the stress which originates from the difference in thermal expansion coefficient of the layers.
In Examined Published Japanese Patent Application No. 8-8201 is disclosed adding a borosilicate glass containing an alkaline earth oxide into the ceramic dielectric material and/or the ceramic magnetic material in order to approximate the linear expansion of one material to that of the other. In this case again, the object of the addition of the glass component is to relax the stress which results from the difference in thermal expansion coefficient.
As described above, the effect that is expected by adding a borosilicate glass into the dielectric ceramic material and/or the magnetic ceramic material is controlling the thermal expansion coefficient of the capacitor portion and the inductor portion by complexing the thermal expansion coefficients of the dielectric ceramic material and the magnetic ceramic material.
To cope with the wide range of thermal expansion coefficient, however, this method of changing the thermal expansion coefficient of the glass alone has difficulties or limits. The thermal expansion coefficient of a borosilicate glass can be changed by changing the composition and the compositional ratio of the glass. However, the change in composition and compositional ratio influences the physical and chemical properties of the borosilicate glass. In particular, the glass viscosity, whose effective index is the softening point of glass, is greatly affected. The change in viscosity also changes the sinterability of the capacitor and the inductor portions. Accordingly, a change in thermal expansion signifies a change in sintering temperature as well, and generates defects such as peeling and warping on the monolithically sintered product component.
Furthermore, the above disclosures describe nothing on the influence of glass on the joining properties between the dielectric ceramic material and magnetic ceramic material into which the glass is added. In fact, by changing the composition and the compositional ratio of glass, and thereby changing the viscosity of the glass, the interdiffusion rate and the reactivity of the components change between the capacitor portion and the inductor portion to affect the joining properties.
Moreover, although depending on the compositional ratio, the borosilicate glass that is contained in the dielectric ceramic layer and the magnetic ceramic layer may undergo degradation in resistances against moisture, acids, and alkalis. The incorporation of B.sub.2 O.sub.3 is a cause of bringing about such a degradation on the glass. This effect can be observed particularly in the SiO.sub.2 -poor regions. The loss in reliability on the glass by the incorporation of B.sub.2 O.sub.3 may lead to a vital defect for LC composite components by inducing, for instance, interlayer migration in the dielectric ceramic layers of the capacitor portion.